The invention relates to communications systems having redundant channels used in wells.
After a wellbore has been drilled, various completion operations may be performed in the wellbore, in which equipment including packers, valves, flow tubes, and other devices may be set to control fluid production from one or more zones in the well. With advances in technology, sensing and control devices may be placed downhole to monitor and to adjust equipment settings as needed.
A system that monitors downhole conditions may include various downhole gauges and sensors that are capable of monitoring temperature, pressure, and flow information. Using a communications link, such as an acoustic data link or a digital telemetry link, data gathered by the gauges and sensors may be sent to the surface to control boxes. The data may then be processed to determine conditions downhole so that production may be improved and potential reservoir problems may be avoided. In addition to gauges and sensors, downhole systems may include control devices capable of receiving commands from the surface for controlling equipment settings downhole.
To communicate information to the surface and to transmit commands downhole, a communications link may be coupled to multiple nodes positioned at various depths and in different completion zones. Because of the long lengths of a communications link in a well (typically thousands of feet to tens of thousands of feet long) and the relatively harsh environment downhole, portions of the communications link may be subject to failure. Failures may include, as examples, mechanical breakage of a portion of the communications link, shorting of electrical conductors in the link, or other types of failures. Further, the nodes themselves may fail, which may prevent communication to other nodes in the well. Failure of nodes may be caused by loss of power or well fluid flooding, for example.
Communications systems have included redundant communications links to provide some fault tolerance. In one conventional system, two channels are coupled between successive nodes. If one channel fails, the other takes over. However, with this scheme, failure of a node may prevent further communication to downstream nodes from the surface. Thus, a need exists for communications systems with improved fault tolerance.
In general, according to one embodiment, a communications system in a well having downhole nodes coupled by a communications link is set up. Existence of a node failure is determined, and if so, an alternate route is identified in the communications link around the failed node.
Other features will become apparent from the following description and from the claims.